Units (Radioactivity)

2 marks · Hard

In an investigation of half-life, you are told to record the 'interval' for each measurement of activity and to keep the apparatus at the same separation throughout. Name the correct units you would use to record (i) the time interval between measurements and (ii) the separation between the radioactive source and detector. Briefly justify your answers.

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(i) minutes (min) or seconds (s) for time interval, (ii) centimetres (cm) for separation, because these are the syllabus-required units for time and distance in radioactivity experiments.

Also accept: Accept 'second(s)' for time and 'centimetre(s)' for separation, with a short justification referencing syllabus

Common mistakes: Using hours or metres, or omitting justification

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Marking points

B1 · 1 mark · Correctly states minutes (min) or seconds (s) for the time interval, justified by syllabus.

B1 · 1 mark · Correctly states centimetres (cm) for separation, justified by syllabus.

Worked solution

(i) Time interval: minutes (min) or seconds (s) — these are the recommended units for time in radioactivity experiments. (ii) Separation between source and detector: centimetres (cm) — this is the syllabus-required unit for distance.